Targeted therapies (kinase inhibitors) US Medical PG Practice Questions and MCQs
Practice US Medical PG questions for Targeted therapies (kinase inhibitors). These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Targeted therapies (kinase inhibitors) US Medical PG Question 1: A research team develops a new monoclonal antibody checkpoint inhibitor for advanced melanoma that has shown promise in animal studies as well as high efficacy and low toxicity in early phase human clinical trials. The research team would now like to compare this drug to existing standard of care immunotherapy for advanced melanoma. The research team decides to conduct a non-randomized study where the novel drug will be offered to patients who are deemed to be at risk for toxicity with the current standard of care immunotherapy, while patients without such risk factors will receive the standard treatment. Which of the following best describes the level of evidence that this study can offer?
- A. Level 1
- B. Level 3 (Correct Answer)
- C. Level 5
- D. Level 4
- E. Level 2
Targeted therapies (kinase inhibitors) Explanation: ***Level 3***
- A **non-randomized controlled trial** like the one described, where patient assignment to treatment groups is based on specific characteristics (risk of toxicity), falls into Level 3 evidence.
- This level typically includes **non-randomized controlled trials** and **well-designed cohort studies** with comparison groups, which are prone to selection bias and confounding.
- The study compares two treatments but lacks randomization, making it Level 3 evidence.
*Level 1*
- Level 1 evidence is the **highest level of evidence**, derived from **systematic reviews and meta-analyses** of multiple well-designed randomized controlled trials or large, high-quality randomized controlled trials.
- The described study is explicitly stated as non-randomized, ruling out Level 1.
*Level 2*
- Level 2 evidence involves at least one **well-designed randomized controlled trial** (RCT) or **systematic reviews** of randomized trials.
- The current study is *non-randomized*, which means it cannot be classified as Level 2 evidence, as randomization is a key criterion for this level.
*Level 4*
- Level 4 evidence includes **case series**, **case-control studies**, and **poorly designed cohort or case-control studies**.
- While the study is non-randomized, it is a controlled comparative trial rather than a case series or retrospective case-control study, placing it at Level 3.
*Level 5*
- Level 5 evidence is the **lowest level of evidence**, typically consisting of **expert opinion** without explicit critical appraisal, or based on physiology, bench research, or animal studies.
- While the drug was initially tested in animal studies, the current human comparative study offers a higher level of evidence than expert opinion or preclinical data.
Targeted therapies (kinase inhibitors) US Medical PG Question 2: A 56-year-old African American presents to the emergency department due to abdominal pain, fatigue, and weight loss over the past 3 months. He has a long-standing history of chronic hepatitis B virus infection complicated by cirrhosis. On examination, he has jaundice, leg edema, and a palpable mass in the right upper abdominal quadrant. Abdominal ultrasound shows a 3-cm liver mass with poorly defined margins and coarse, irregular internal echoes. Blood investigations are shown:
Aspartate aminotransferase (AST) 90 U/L
Alanine aminotransferase (ALT) 50 U/L
Total bilirubin 2 mg/dL
Albumin 3 g/dL
Alkaline phosphatase 100 U/L
Alpha fetoprotein 600 micrograms/L
Which of the following targeted agents is approved for advanced-stage hepatoma?
- A. Ustekinumab
- B. Daclizumab
- C. Sorafenib (Correct Answer)
- D. Abciximab
- E. Palivizumab
Targeted therapies (kinase inhibitors) Explanation: ***Sorafenib***
- This patient's presentation with chronic hepatitis B, cirrhosis, a liver mass, and an **elevated alpha-fetoprotein** is highly suggestive of **hepatocellular carcinoma (HCC)**, also known as hepatoma.
- **Sorafenib** is a **multi-targeted tyrosine kinase inhibitor** that inhibits tumor cell proliferation and angiogenesis by targeting VEGFR, PDGFR, Raf kinases, and other kinases involved in tumor progression.
- It was the **first systemic therapy approved for advanced-stage HCC** and remains an important first-line treatment option for patients with advanced disease who are not candidates for surgical or locoregional therapies.
*Ustekinumab*
- **Ustekinumab** is a monoclonal antibody that targets the **p40 subunit of IL-12 and IL-23**, primarily used in the treatment of **psoriasis** and psoriatic arthritis, not HCC.
- It works by blocking inflammatory pathways involved in autoimmune conditions.
*Daclizumab*
- **Daclizumab** is a humanized monoclonal antibody that targets the **CD25 subunit of the IL-2 receptor**; it was previously used for treating **multiple sclerosis** but has been largely discontinued due to safety concerns.
- It is not indicated for the treatment of any form of cancer.
*Abciximab*
- **Abciximab** is a monoclonal antibody that targets the **glycoprotein IIb/IIIa receptor** on platelets, used as an **antiplatelet agent** in patients undergoing percutaneous coronary intervention.
- Its mechanism of action is related to inhibition of platelet aggregation and thrombosis, not cancer therapy.
*Palivizumab*
- **Palivizumab** is a monoclonal antibody used for the **prevention of serious lower respiratory tract disease** caused by **respiratory syncytial virus (RSV)** in high-risk infants.
- It provides passive immunity against RSV and has no role in cancer treatment.
Targeted therapies (kinase inhibitors) US Medical PG Question 3: A 71-year-old woman presents to her hematologist-oncologist for follow up after having begun doxorubicin and cyclophosphamide in addition to radiation therapy for the treatment of her stage 3 breast cancer. Her past medical history is significant for preeclampsia, hypertension, polycystic ovarian syndrome, and hypercholesterolemia. She currently smokes 1 pack of cigarettes per day, drinks a glass of wine per day, and denies any illicit drug use. The vital signs include: temperature 36.7°C (98.0°F), blood pressure 126/74 mm Hg, heart rate 111/min, and respiratory rate 23/min. On physical examination, the pulses are strong and irregular, she has a grade 3/6 holosystolic murmur heard best at the left upper sternal border, clear bilateral breath sounds, and erythema over her site of radiation. Which of the following statements regarding doxorubicin is true?
- A. Doxorubicin has a maximum lifetime dose, due to the risk of cardiac toxicity (Correct Answer)
- B. Doxorubicin has a maximum lifetime dose, due to the risk of pulmonary toxicity
- C. Doxorubicin will increase her risk for deep vein thrombosis (DVT) and pulmonary embolism (PE)
- D. Doxorubicin frequently causes an acneiform rash
- E. Doxorubicin frequently causes cystitis
Targeted therapies (kinase inhibitors) Explanation: ***Doxorubicin has a maximum lifetime dose, due to the risk of cardiac toxicity***
- **Doxorubicin** is a potent chemotherapy agent (anthracycline) with a well-known risk of **cardiotoxicity**, which can lead to **dilated cardiomyopathy** and heart failure.
- To mitigate this severe side effect, a **cumulative lifetime dose limit** (usually 450-550 mg/m²) is established for doxorubicin.
*Doxorubicin has a maximum lifetime dose, due to the risk of pulmonary toxicity*
- While some chemotherapy agents can cause pulmonary toxicity, **doxorubicin** is not primarily associated with this as its main dose-limiting toxicity.
- The most significant and common dose-limiting toxicity of doxorubicin is **cardiotoxicity**, not pulmonary.
*Doxorubicin will increase her risk for deep vein thrombosis (DVT) and pulmonary embolism (PE)*
- Chemotherapy in general can increase the risk of **thromboembolic events**, but this is not a specific dose-limiting toxicity of **doxorubicin** that dictates a lifetime maximum dose.
- The concern for DVT/PE is a broader complication of cancer and its treatment, distinct from doxorubicin's specific cardiac risk.
*Doxorubicin frequently causes an acneiform rash*
- **Acneiform rash** is a common side effect of epidermal growth factor receptor (EGFR) inhibitors (e.g., cetuximab, erlotinib), not typically associated with **doxorubicin**.
- Doxorubicin's dermatologic side effects usually involve **alopecia**, hand-foot syndrome, and radiation recall, but not a predominant acneiform rash.
*Doxorubicin frequently causes cystitis*
- **Cystitis**, particularly hemorrhagic cystitis, is a well-known side effect of **cyclophosphamide** (another drug the patient is receiving), not **doxorubicin**.
- **Mesna** is often administered with cyclophosphamide to prevent this urological toxicity.
Targeted therapies (kinase inhibitors) US Medical PG Question 4: A 62-year-old woman presents to her oncologist to discuss the chemotherapy options for her newly diagnosed breast cancer. During the meeting, they discuss a drug that inhibits the breakdown of mitotic spindles in cells. Her oncologist explains that this will be more toxic to cancer cells because those cells are dividing more rapidly. Which of the following side effects is closely associated with the use of this chemotherapeutic agent?
- A. Photosensitivity
- B. Peripheral neuropathy (Correct Answer)
- C. Paralytic ileus
- D. Hemorrhagic cystitis
- E. Pulmonary fibrosis
Targeted therapies (kinase inhibitors) Explanation: ***Peripheral neuropathy***
- Drugs that inhibit the breakdown of **mitotic spindles** are **microtubule-targeting agents** (e.g., **taxanes** like paclitaxel/docetaxel, **vinca alkaloids** like vincristine/vinblastine).
- These agents interfere with **microtubule function** in neurons, leading to **axonal damage** and **peripheral neuropathy**.
- This is the **most characteristic and common dose-limiting toxicity** of microtubule inhibitors, affecting sensory and motor nerves (numbness, tingling, weakness in extremities).
*Photosensitivity*
- **Photosensitivity** is a common adverse effect associated with certain chemotherapeutic agents like **fluorouracil** (5-FU) or **methotrexate**, but is not linked to microtubule inhibitors.
- It involves an increased sensitivity to UV light, often manifesting as a rash or exaggerated sunburn.
*Paralytic ileus*
- **Paralytic ileus** can occur with **vinca alkaloids** (especially vincristine) due to autonomic neuropathy affecting the **enteric nervous system**.
- However, this is **less common** than peripheral neuropathy and occurs more specifically with vincristine rather than taxanes.
- **Peripheral neuropathy** is the more pervasive, dose-limiting, and universally characteristic side effect across all microtubule inhibitors.
*Hemorrhagic cystitis*
- **Hemorrhagic cystitis** is a classic side effect of **alkylating agents** like **cyclophosphamide** and **ifosfamide**, which produce the toxic metabolite **acrolein**.
- It is prevented/managed with **mesna**, which inactivates acrolein.
- Not associated with microtubule inhibitors.
*Pulmonary fibrosis*
- **Pulmonary fibrosis** is a known side effect of certain chemotherapeutic drugs, most notably **bleomycin** and **busulfan**.
- This adverse effect is not associated with agents that target **mitotic spindle breakdown**.
Targeted therapies (kinase inhibitors) US Medical PG Question 5: A 47-year-old woman presents to the physician with complaints of fatigue accompanied by symmetric pain, swelling, and stiffness in her wrists, fingers, knees, and other joints. She describes the stiffness as being particularly severe upon awakening, but gradually improves as she moves throughout her day. Her physician initially suggests that she take NSAIDs. However, after a few months of minimal symptomatic improvement, she is prescribed an immunosuppressive drug that has a mechanism of preventing IL-2 transcription. What is the main toxicity that the patient must be aware of with this particular class of drugs?
- A. Pancytopenia
- B. Osteoporosis
- C. Hepatotoxicity
- D. Nephrotoxicity (Correct Answer)
- E. Hyperglycemia
Targeted therapies (kinase inhibitors) Explanation: ***Nephrotoxicity***
- The drug described, which prevents **IL-2 transcription**, is likely a **calcineurin inhibitor** like cyclosporine or tacrolimus, often used in autoimmune diseases.
- **Nephrotoxicity** (kidney damage) is a major dose-limiting toxicity of calcineurin inhibitors, causing both acute and chronic kidney injury.
*Pancytopenia*
- While some immunosuppressants can cause **pancytopenia** (e.g., azathioprine, methotrexate), it is not the classic or primary toxicity associated with calcineurin inhibitors.
- Calcineurin inhibitors primarily affect **renal function** and can cause other side effects like hypertension or neurotoxicity.
*Osteoporosis*
- **Osteoporosis** is a known side effect of long-term glucocorticoid use, but not typically a primary toxicity of calcineurin inhibitors.
- Glucocorticoids reduce bone formation and increase bone resorption, leading to bone density loss.
*Hepatotoxicity*
- **Hepatotoxicity** (liver damage) can occur with various immunosuppressants, such as methotrexate, but it is not the most prominent or defining toxicity for calcineurin inhibitors.
- While cyclosporine can cause some liver enzyme elevation, **nephrotoxicity** is far more common and severe.
*Hyperglycemia*
- **Hyperglycemia** can be a side effect of some immunosuppressants, particularly **glucocorticoids** and **tacrolimus** (another calcineurin inhibitor).
- However, for the class of drugs that prevent IL-2 transcription (calcineurin inhibitors), **nephrotoxicity** remains the most significant and common major toxicity to be aware of.
Targeted therapies (kinase inhibitors) US Medical PG Question 6: A 78-year-old man receives chemotherapy for advanced hepatocellular carcinoma. Despite appropriate therapy, he dies 4 months later. Histopathological examination of the cancer cells shows the presence of a transmembrane efflux pump protein that is known to cause decreased intracellular concentrations of chemotherapeutic drugs. Which of the following best describes this membrane protein?
- A. G protein
- B. Cadherin
- C. P-glycoprotein (Correct Answer)
- D. Tyrosine receptor
- E. Channel protein
Targeted therapies (kinase inhibitors) Explanation: **P-glycoprotein**
- **P-glycoprotein** (also known as **MDR1**) is a well-known **efflux pump** that actively transports many chemotherapy drugs out of cancer cells, leading to **multidrug resistance**.
- Its presence explains the **decreased intracellular concentrations** of chemotherapy drugs and the poor response to treatment in this patient.
*G protein*
- **G proteins** are intracellular signaling molecules that mediate responses to various extracellular stimuli, not primarily involved in drug efflux.
- They are typically associated with **G protein-coupled receptors** and downstream signaling pathways, not direct drug transport.
*Cadherin*
- **Cadherins** are cell adhesion molecules that play a crucial role in cell-cell binding and maintaining tissue structure.
- They are not involved in the active transport of drugs across the cell membrane.
*Tyrosine receptor*
- **Tyrosine kinase receptors** are transmembrane proteins that bind to growth factors and initiate intracellular signaling cascades, promoting cell growth and differentiation.
- They are involved in signaling, not in the active transport of chemotherapy drugs out of the cell.
*Channel protein*
- **Channel proteins** facilitate the passive diffusion of ions or small molecules across the cell membrane, typically down their electrochemical gradient.
- While they are transmembrane proteins, they do not actively pump drugs out against a concentration gradient, which is characteristic of multidrug resistance.
Targeted therapies (kinase inhibitors) US Medical PG Question 7: An investigator studying targeted therapy in patients with gastrointestinal stromal tumors requires a reliable test to determine the spatial distribution of CD117-positive cells in biopsy specimens. Which of the following is the most appropriate test?
- A. Northern blot
- B. Immunohistochemistry (Correct Answer)
- C. Flow cytometry
- D. Fluorescence in-situ hybridization
- E. Western blot
Targeted therapies (kinase inhibitors) Explanation: ***Immunohistochemistry***
- **Immunohistochemistry (IHC)** uses **antibodies** to target specific antigens (like **CD117**) within tissue sections, allowing for **visualization of their spatial distribution** under a microscope.
- This technique is ideal for identifying the precise location and quantity of **CD117-positive cells** within a biopsy, which is crucial for assessing targeted therapy in gastrointestinal stromal tumors.
*Northern blot*
- **Northern blot** is used to detect and quantify specific **RNA** sequences in a sample.
- It does not provide information about **protein expression** or the **spatial distribution of cells** within tissue.
*Flow cytometry*
- **Flow cytometry** is used for analyzing and sorting cells based on their **surface or intracellular markers** by passing them in a fluid stream through laser light.
- While it can quantify **CD117-positive cells**, it requires cells to be in suspension and thus **destroys the tissue architecture**, preventing analysis of spatial distribution.
*Fluorescence in-situ hybridization*
- **Fluorescence in-situ hybridization (FISH)** uses **fluorescent probes** to detect and locate specific **DNA or RNA sequences** on chromosomes or in cells.
- FISH is primarily used for genetic analysis and **does not directly assess protein expression** or cellular distribution in the context of targeted therapy.
*Western blot*
- **Western blot** is used to detect and quantify specific **proteins** from a sample by separating them by size, but it is performed on **tissue homogenates**.
- This technique provides information on the **total protein content** but **does not preserve the spatial arrangement** of cells within the original tissue.
Targeted therapies (kinase inhibitors) US Medical PG Question 8: A 55-year-old man comes to the physician because of a 4-month history of fatigue, increased sweating, and a 5.4-kg (12-lb) weight loss. Over the past 3 weeks, he has had gingival bleeding when brushing his teeth. Twenty years ago, he was diagnosed with a testicular tumor and treated with radiation therapy. His temperature is 37.8°C (100°F), pulse is 70/min, respirations are 12/min, and blood pressure is 130/80 mm Hg. He takes no medications. Cardiopulmonary examination shows no abnormalities. The spleen is palpated 4 cm below the left costal margin. Laboratory studies show:
Hemoglobin 9 g/dL
Mean corpuscular volume 86 μm3
Leukocyte count 110,000/mm3
Segmented neutrophils 24%
Metamyelocytes 6%
Myelocytes 34%
Promyelocytes 14%
Blasts 1%
Lymphocytes 11%
Monocytes 4%
Eosinophils 4%
Basophils 2%
Platelet count 650,000/mm3
Molecular testing confirms the diagnosis. Which of the following is the most appropriate next step in treatment?
- A. Phlebotomy
- B. Cytarabine and daunorubicin therapy
- C. Rituximab therapy
- D. Low-dose aspirin therapy
- E. Imatinib therapy (Correct Answer)
Targeted therapies (kinase inhibitors) Explanation: ***Imatinib therapy***
- The patient's presentation with **fatigue**, **sweating**, **weight loss**, **gingival bleeding**, **splenomegaly**, and remarkable lab findings (**leukocytosis** with a left shift including **myelocytes**, **promyelocytes**, low blast count, **thrombocytosis**, and **anemia**) is highly suggestive of **Chronic Myeloid Leukemia (CML)**.
- Molecular testing would confirm the presence of the **Philadelphia chromosome (BCR-ABL1 fusion gene)**, which is the target of **imatinib**, a tyrosine kinase inhibitor (TKI) and the first-line treatment for CML.
*Phlebotomy*
- **Phlebotomy** is a treatment for **polycythemia vera**, a myeloproliferative neoplasm characterized by an *elevated red blood cell count*, which is not present here (patient has anemia).
- It aims to reduce blood viscosity and iron overload, which are not the primary issues in this patient.
*Cytarabine and daunorubicin therapy*
- This combination therapy (often termed "7+3" regimen) is standard induction chemotherapy for **Acute Myeloid Leukemia (AML)**.
- The patient's **low blast count (1%)** and presence of various myeloid precursor stages define a chronic phase of a myeloproliferative neoplasm, not acute leukemia (which requires >20% blasts).
*Rituximab therapy*
- **Rituximab** is a monoclonal antibody that targets the **CD20 antigen** found on B-cells and is primarily used in the treatment of **B-cell non-Hodgkin lymphomas** and **Chronic Lymphocytic Leukemia (CLL)**.
- This patient presents with a myeloid proliferation, not a lymphoid malignancy.
*Low-dose aspirin therapy*
- **Low-dose aspirin** is used for its antiplatelet effects to prevent thrombotic events, particularly in conditions like **essential thrombocythemia** or **polycythemia vera** where platelet counts or red cell mass are significantly elevated sometimes requiring aspirin if clots are forming.
- While this patient has thrombocytosis, treating the underlying CML with imatinib is the priority and will typically normalize platelet counts, making aspirin a secondary or adjunct consideration if thrombosis risk is high and CML treatment is not yet effective.
Targeted therapies (kinase inhibitors) US Medical PG Question 9: A 54-year-old woman presents to the emergency department with sudden shortness of breath. A CT scan shows multiple nodules in her left lung. She reports that for the past 6 months, she has been feeling tired and depressed. She also has frequently felt flushed, which she presumed is a symptom of getting closer to menopause. On physical examination, a nodule with a size of 2.5 cm is palpable in the left lobe of the thyroid gland; the nodule is firm and non-tender. Cervical lymphadenopathy is present. Cytology obtained by fine needle aspiration indicates a high likelihood of thyroid carcinoma. Laboratory findings show a serum basal calcitonin of 620 pg/mL. A thyroidectomy is performed but the patient presents again to the ER with flushing and diarrhea within 6 weeks. Considering this patient, which of the following treatment options should be pursued?
- A. Observation
- B. Tamoxifen
- C. Vandetanib (Correct Answer)
- D. Radioactive iodine (radioiodine)
- E. Thyroid-stimulating hormone (TSH) suppression
Targeted therapies (kinase inhibitors) Explanation: ***Vandetanib***
- This patient's presentation with **thyroid nodule**, **elevated calcitonin**, and symptoms like flushing and diarrhea, combined with lung metastases, is highly suggestive of **medullary thyroid carcinoma (MTC)**. The recurrence of flushing and diarrhea post-thyroidectomy indicates **persistent or metastatic disease**.
- **Vandetanib** is a multi-kinase inhibitor specifically approved for the treatment of **symptomatic or progressive medullary thyroid carcinoma** that is unresectable or metastatic. It targets key pathways involved in MTC proliferation and angiogenesis, offering a systemic treatment option for advanced disease.
*Observation*
- **Observation** is not appropriate for metastatic medullary thyroid carcinoma, especially given the patient's persistent and symptomatic disease with lung metastases and systemic symptoms.
- MTC is an aggressive cancer, and untreated metastatic disease would lead to continued progression and worsening symptoms.
*Tamoxifen*
- **Tamoxifen** is a selective estrogen receptor modulator primarily used in the treatment of **estrogen receptor-positive breast cancer**.
- It has no role or efficacy in the treatment of medullary thyroid carcinoma.
*Radioactive iodine (radioiodine)*
- **Radioactive iodine (RAI) therapy** is effective for differentiated thyroid cancers (papillary and follicular) because these cancers retain the ability to absorb iodine.
- **Medullary thyroid carcinoma** originates from parafollicular C cells and does not take up iodine, rendering RAID therapy ineffective.
*Thyroid-stimulating hormone (TSH) suppression*
- **TSH suppression therapy** is used in differentiated thyroid cancers to reduce the growth stimulus provided by TSH, thereby reducing recurrence risk.
- **Medullary thyroid carcinoma** does not arise from TSH-dependent thyroid follicular cells, so TSH suppression therapy is not effective for MTC.
Targeted therapies (kinase inhibitors) US Medical PG Question 10: A 55-year-old man presents to his primary care physician for diarrhea. He states that he has experienced roughly 10 episodes of non-bloody and watery diarrhea every day for the past 3 days. The patient has a past medical history of IV drug abuse and recently completed treatment for an abscess with cellulitis. His vitals are notable for a pulse of 105/min. Physical exam reveals diffuse abdominal discomfort with palpation but no focal tenderness. A rectal exam is within normal limits and is Guaiac negative. Which of the following is the best initial treatment for this patient?
- A. Oral rehydration and discharge
- B. Vancomycin (Correct Answer)
- C. Clindamycin
- D. Fidaxomicin
- E. Metronidazole
Targeted therapies (kinase inhibitors) Explanation: ***Vancomycin***
- This patient's recent **antibiotic exposure** (for abscess and cellulitis) combined with **watery diarrhea** (10 episodes/day) and tachycardia (pulse 105/min) strongly suggests **Clostridioides difficile infection (CDI)**.
- **Oral vancomycin** (125 mg PO four times daily × 10 days) is a first-line treatment for initial CDI per current IDSA guidelines and remains the most commonly used agent in clinical practice.
- While fidaxomicin is also first-line (and preferred by guidelines due to lower recurrence rates), vancomycin is more widely available, cost-effective, and equally effective for initial treatment, making it the best initial choice in most clinical settings.
*Oral rehydration and discharge*
- While **oral rehydration** is important for managing dehydration secondary to diarrhea, it is insufficient as the sole treatment given the high clinical suspicion for **CDI**.
- CDI requires targeted antibiotic therapy; discharging with only supportive care risks disease progression, toxic megacolon, and potentially life-threatening complications.
*Clindamycin*
- **Clindamycin** is one of the antibiotics **most strongly associated** with causing **CDI** because it significantly disrupts normal colonic flora.
- Administering clindamycin would worsen the suspected CDI and is absolutely contraindicated in this clinical scenario.
*Fidaxomicin*
- **Fidaxomicin** (200 mg PO twice daily × 10 days) is an excellent antibiotic for **CDI** and is actually recommended as first-line therapy alongside vancomycin in current IDSA guidelines.
- It has advantages including **lower recurrence rates** and better microbiome preservation compared to vancomycin.
- However, in practice, it is less commonly used as initial therapy due to **significantly higher cost** (often >$3,000 vs. <$100 for vancomycin) and more limited availability.
- For exam purposes and typical clinical practice, **vancomycin remains the preferred first-line agent** for initial CDI treatment.
*Metronidazole*
- **Metronidazole** was previously a first-line treatment for **non-severe CDI**, but current IDSA guidelines (2018/2021) no longer recommend it as first-line therapy.
- It has **inferior efficacy** compared to vancomycin and fidaxomicin and is now reserved only for situations where neither vancomycin nor fidaxomicin is available.
- Studies have shown higher treatment failure rates and recurrence rates with metronidazole compared to vancomycin.
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